The present invention relates generally to solid freeform fabrication of objects and, more specifically, to solid freeform fabrication of objects employing electron beam energy.
The basic problem was the lack of a portable, low mass, low power apparatus capable of three-dimensional replacement part fabrication, especially as it applies to remote locations where spare parts are not logistically available. Applications include use for on-site part and tool fabrication for sea-faring ships, oil rigs, mobile military or exploration units, lab-scale systems for research and development environments, and isolated settlements.
Production of replacement components by solid freeform fabrication processes during an extended duration mission or in remote locations could reduce or eliminate the need to carry a complete inventory of pre-manufactured spares. For example, future long-duration human space exploration missions will be challenged by constraints on mass and volume allocations available for spare parts. Addressing this challenge is critical to the success of these missions. As a result, it is continually necessary to consider new approaches to spacecraft maintenance and repair that minimize the mass and stowage volume that must be allocated for spares while enhancing mission robustness. For example, rather than having to stow numerous spares, replacement components would be generated as needed from feedstock material. As a result, only the total mass of replacements would need to be estimated instead of a prediction of which specific components might be required. Attempting to predict which components will fail and require replacement is inherently an inaccurate process and will certainly result in provisioning numerous components that will never be used (wasted mass and wasted volume) and may result in under-provisioning of other components. This technology could also be used to support fabrication of large structures and repair of primary structures as well as structural and mechanical components.
Direct deposition processes utilizing electron beam energy sources offer the greatest potential for remote applications. Conventional electron beam welding operating in the range of about 60 kV accelerating voltage generates sufficient radiation to pose a serious potential health risk to personnel. This hazard is controlled by incorporating sufficient shielding in the walls and windows of the sealed container. Clearly, massive shielding would be counter to the objective of developing a lightweight, portable system. Further, the mass associated with this shielding would be a very undesirable characteristic for an operational system to be used onboard spacecraft. Since heavy shielding is undesirable in this application, the alternative approach is to design the process in such a way that production of hazardous penetrating radiation is avoided. This can be accomplished by operating at significantly lower accelerating voltages than are typically used for industrial electron beam welding. Operation in the range from about 8 to about 15 kV will minimize production of penetrating radiation. Shielding provided by a simple stainless steel or aluminum sealed container should be adequate to ensure the safety of operating personnel.
Although the feedstock material can be introduced as either a powder or wire, the wire form is preferable for both terrestrial and interplanetary applications. Specifically, for interplanetary space applications, wire feedstock is preferable due to operational and safety issues associated with management of metallic powder in a microgravity environment. However, powder form feedstock is feasible for terrestrial applications.
Because of superior energy conversion efficiency compared with laser systems, electron beam technology is the preferred means.
The present apparatus and method for use described herein can be utilized in a very rapid and economic fashion to produce, for example, tools, parts, products, or molds per a user's production requirements. The present apparatus and method for use attempts to overcome the aforementioned problems and challenges.